Many times, partner disputes and litigation involve “escalating” the issue to the courts.
If it’s about e-commerce, digital promotion, and similar issues, the contestants sometimes end up having to provide expert witnesses on their own behalf, in order to estimate damages or establish any negligence.
So in most cases, the lawyer is looking for a witness capable of providing the court with expert opinion and even appear before court to testify. (just like a real estate assessor or a medical doctor seeking to establish medical negligence).
There is more than one way to work with the expert witness, however time and experience have taught me the way that’s right for me. Let me break it by steps:

Step 1: Initial review of the case
A legitimate expert witness wouldn’t instantly agree to testify on any matter and personally I answer with more “No”s than “Yes”s, and I have to learn the case before either accepting or rejecting it. At this point I would meet with the contestants, asking them to bring to the meeting any meaningful papers they have on the matter (contracts, statements, correspondence, etc.) and to have the attorney present as well. My question to the attorney is “which claims would you like me to support”.
After the meeting and learning the case I dive into the documents, facts, and hypotheses and determine whether I can support all, some, or none of the claims.
This is a crucial, essential step for both the witness and litigants, since it can save precious time and money. Nothing is worse than having a witness tell the litigants, after being selected and having learned the case, that they won’t be able to support the litigants’ claims.
At this point, the witness doesn’t have all the materials, so their answer just might be “if I can’t find a document refuting this claim or if I see this or that paper, I’d be able to support the claim”.

Step 2: Executing the agreement
The execution of the agreement between the expert witness and the contestants, usually validating the pay, schedule, and form in which the expert’s opinion is to be received.
Step 3: Submitting all documents and credentials
At this point, you should submit all available materials, including account login credentials (Amazon, Google, etc.). It’s extremely important not to keep any documents from the witness (especially following the discovery of documents). In the worst possible scenario for both the witness and you, the opposing counsel reveals a document not yet seen by your witness, undermining your witness’s credibility and your case.
Step 4: Receiving expert opinion
In most cases, expert opinion would be provided and signed in PDF format. This step my be preceded by some back and forth on certain matters.

Conclusion:
Personally speaking, I would always recommend to avoid ending up in court, trying mediation or arbitration first. Sometimes there’s no avoiding legal procedures. For the opinion of your expert to be well-received, you must make sure that they are indeed experts in their field and that they have some understanding and experience with providing expert opinion. In many legal cases, the entire weight falls on the shoulders of your expert.